CN1680513A

CN1680513A - Fluorescent material and fluorescent display apparatus

Info

Publication number: CN1680513A
Application number: CNA2005100697191A
Authority: CN
Inventors: 大岛英纪; 佐藤冬季; 窪田俊一
Original assignee: Noritake Co Ltd
Current assignee: Noritake Co Ltd
Priority date: 2004-03-30
Filing date: 2005-03-29
Publication date: 2005-10-12
Anticipated expiration: 2025-03-29
Also published as: US20050218782A1; US7416685B2; CN100554371C; KR20060045148A; JP4217648B2; JP2005281507A

Abstract

A CaTiO3: Pr,M fluorescent material including 100 mol % of calcium titanate CaTiO3 as a host crystal; from 0.003 mol % to 0.05 mol % of praseodymium Pr which is added, as a first additive, to the host crystal; and at least one of aluminum Al, gallium Ga, indium In, zinc Zn, magnesium Mg, sodium Na, and potassium K which is added, as a second additive M, to the host crystal.

Description

Fluorescent material and fluorescent display device

Cross Reference to Related Applications

The present application is based on Japanese patent application 2004-097738, filed 3/30/2004, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to a fluorescent material, and a fluorescent display device including the fluorescent material as a light source.

Background

Zn is generally known_1-xCd_xAn S fluorescent material (hereinafter referred to as ZnCdS fluorescent material) is used as a red light emitting fluorescent material excited by a low voltage electron beam, and is used in a fluorescent display device such as a Vacuum Fluorescent Display (VFD). Recently, however, in consideration of environmental quality, harmful elements such as cadmium CdThe use of ZnCdS phosphor is limited, which is the limit. In addition, the ZnCdS fluorescent material as a sulfide is decomposed when exposed to an electron beam, and sulfur S dispersed from the sulfide may reduce the electron emission capability of an oxide cathode as an electron source. Unless otherwise defined, reference herein to a "low voltage electron beam" is a reference to an electron beam suitable for use in a VFD that is accelerated by a voltage of from about 10V to about 100V.

In the above-mentioned background art, an oxide fluorescent material that does not contain cadmium Cd or sulfur S has been proposed, and emits red light in response to a low-voltage electron beam. More specifically, the oxide fluorescent material as the host crystal includes oxides of alkaline earth metal and titanium Ti, and rare earth element and group 3 element each as an additive. The alkaline earth metal can be magnesium Mg, strontium Sr, calcium Ca or barium Ba; the rare earth element can be cerium Ce, praseodymium Pr, europium Eu, terbium Tb, erbium Er or thulium Tm; and the group 3 element may be aluminum Al, gallium Ga, indium In, or thallium Tl. Typical compositions of the above-mentioned oxide fluorescent materials maySo as to be SrTiO₃Pr, Al, which is disclosed in patent document 1 (Japanese patent application laid-open No. 8-85788) or patent document 2 (Japanese patent application laid-open No. 2003-41246). Here, in the column "" the right element Pr, Al means strontium titanate SrTiO added as a matrix crystal₃Component (b) or element (b). According to patent document 1, the composition preferably includes 0.1 to 2 mol% of praseodymium Pr and 1 to 50 mol% of aluminum.

In addition, CaTiO is also proposed₃A fluorescent material, as an example of a composition in which the alkaline earth metal is calcium Ca, although the fluorescent material cannot be used in VFD. CaTiO₃Fluorescent materials are disclosed in non-patent document 1(Vecht et al, "New electronic exposed light emitting materials" J.Vac.Sci.Technol.B 12 (2); Mar/Apr 1994 p.781-784), non-patent document 2(P.T.Diallo et al, "Improvement of the optical characteristics of Pr. Referring to FIGS³⁺inCaTiO₃"Journal of Alloys and Compounds 323-₃:Pr⁺³”EURODISPLAY 2002 p.777-779)。

Disclosure of Invention

However, the SrTiO disclosed in patent document 1₃Pr and Al fluorescent materials have the problems of rapid brightness decline and short life expectancy. Patent document 2 discloses a technique in which luminance degradation is reduced by providing a protective layer formed of a host compound or crystal on the particle surface of a fluorescent material. However, although the protective layer is provided, SrTiO₃Pr, Al fluorescent materials have much shorter life expectancy than ZnCdS fluorescent materials. In addition, SrTiO of the protective layer is used even at the initial stage of use₃Pr, Al phosphors show lower brightness than ZnCdS phosphors.

In addition, if the CaTiO disclosed in

non-patent documents

1, 2, and 3₃The fluorescent material is excited by low-voltage electron beam, and CaTiO₃The emission luminance of the phosphor is at most about one tenth of that of the ZnCdS phosphor. Thus, CaTiO₃Fluorescent materials are not suitable for VFDs.

Accordingly, it is an object of the present invention to provide an oxide fluorescent material and a fluorescent display device, which have a lifetime expectancy ratio of SrTiO₃Pr, Al fluorescent materials are long and can emit light of high brightness even when excited by a low-voltage electron beam. This object is achieved by the present invention.

According to a first aspect of the present invention, there is provided a CaTiO₃Pr, M fluorescent material, and package thereofComprises 100mol percent of calcium titanate CaTiO₃As a host crystal; 0.003 mol% to 0.05 mol% of praseodymium Pr is added as a first additive to the matrix crystal; and at least one of aluminum Al, gallium Ga, indium In, zinc Zn, magnesium Mg, sodium Na, and potassium K as a second additive M to be added to the matrix crystal.

According to a second aspect of the present invention, there is provided a fluorescent display device comprising the CaTiO according to the first aspect of the present invention₃Pr, M fluorescent material as light source.

In the CaTiO according to the first aspect of the invention₃Pr, M fluorescent material, adding 0.003 mol% to 0.05 mol% of praseodymium Pr as an activator to calcium titanate CaTiO as a matrix crystal₃And further adding at least one element M selected from the group consisting of aluminum Al, gallium Ga, indium In, zinc Zn, magnesium Mg, sodium Na, and potassium K. Thereby obtaining an oxide fluorescent material having a life expectancy longer than that of conventional SrTiO₃Pr, Al fluorescent materials are long and can emit light of high brightness even when excited by a low-voltage electron beam. More specifically, since the amount of praseodymium Pr added falls within the above range and the element Pr is used together with, for example, aluminum Al as an additional activator, even though it is possible to excite by a low-voltage electron beam, CaTiO₃Pr, M phosphor can still emit light of highbrightness, however, conventional CaTiO is not excited by high voltage electron beam or ultraviolet ray₃The fluorescent material cannot emit light of high brightness. In addition, the CaTiO of the present invention₃No degradation of Pr, M phosphors₃Pr and Al fluorescent materials are abundant. For example, the CaTiO of the present invention₃The emission luminance of Pr, M phosphor may be conventional CaTiO containing 0.1 mol% of Pr₃Twice as much or more as fluorescent material. Meanwhile, when the amount of praseodymium Pr added is less than 0.003 mol% or more than 0.05 mol%, CaTiO excited by a low-voltage electron beam₃Pr, M fluorescent material is kept significantly lower in light emission luminance than the conventional sulfide fluorescent material, but when the CaTiO is excited by a high-voltage electron beam or ultraviolet ray of not less than 1kV₃Pr, M fluorescent material, high brightness can be obtained.

The reason why the above-mentioned high luminance is obtained is presumed to be that if the concentration of praseodymium Pr is too high, the luminance is lowered due to so-called "concentration quenching"; and as the concentration decreases, the effect of concentration quenching decreases, and thus the brightness increases. On the other hand, if the concentration of praseodymium Pr is too low, the number of luminescent centers of the fluorescent material decreases, and thus the luminance decreases. Thus, it can be presumed that CaTiO according to the first aspect of the present invention₃Pr, M fluorescent material, the optimum concentration range of praseodymium Pr is 0.003 mol% to 0.05 mol%, when the number of luminescent centers is sufficiently large and the level of concentration quenching is highIs sufficiently low.

In addition, CaTiO is presumed to be₃Pr, M fluorescent material lifetime expectancy ratio SrTiO₃Pr, the reason for the long life expectancy of Al phosphors is as follows: under the condition of exciting these fluorescent materials by electron beams, CaTiO₃The amount of oxygen released from the host crystal of Pr, M phosphor is larger than that of SrTiO₃Pr, the host crystal of the Al fluorescent material releases a low amount of oxygen. That is, CaTiO₃The amount ratio of defects in the crystal lattice of Pr, M fluorescent material SrTiO₃Pr, the amount of lattice defects in Al fluorescent materials is less. If the particles of each fluorescent material have lattice defects, the brightness of light emitted from each fluorescent material is reduced. Therefore, it is presumed that CaTiO₃Pr, M fluorescent materials release less oxygen and therefore the material has a lower amount of defects, and thus, CaTiO₃Pr, M fluorescent material lifetime expectancy ratio SrTiO₃Pr, Al fluorescent material is longer.

According to a second aspect of the invention, a fluorescent display device is provided, using the CaTiO according to the first aspect of the invention₃Pr, M fluorescent material as light source. Therefore, the fluorescent display device can operate at low voltage and has a long life expectancy and high light emission luminance.

The term "calcium titanate CaTiO" as referred to in the present application₃The definition of "includes not only compounds having a stoichiometric composition in which the ratio of calcium Ca to titanium Ti is 1, but also compounds in which the ratio is slightly larger or smaller than 1, for example, in a ratio range of 1.05 to 0.95.

The fluorescent material according to the first aspect of the present invention may exhibit high brightness even when excited by a low-voltage electron beam that may be used in a VFD. However, the fluorescent material may be excited by a high voltage electron beam of at least 1kV or ultraviolet rays to emit light. Thus, the fluorescent material can be used in other applications than applications using low-voltage electron beam excitation. More specifically, the fluorescent material of the present invention can be advantageously used for: an FED (field emission display) in which a fluorescent material emits light by being excited by an electron beam generated by a voltage of about 1kV to about 10 kV; a CRT (cathode ray tube) in which a fluorescent material emits light by being excited by an electron beam generated by a voltage of about 10 kV; or a PDP (plasma display panel) in which a fluorescent material emits light by ultraviolet ray excitation. Therefore, the fluorescent display device according to the second aspect of the present invention includes not only a VFD (vacuum fluorescent display), but also an FED, a CRT, and a PDP as long as they use the fluorescent material according to the first aspect of the present invention as a light source.

With respect to the fluorescent material according to the first aspect of the invention, the first additive is added to the host crystalCalcium titanate CaTiO₃The ion valence of praseodymium Pr in (b) may be 3+ or 4 +. However, praseodymium ion Pr³⁺Contributing to the red light. Due to praseodymium ion Pr³⁺Ionic radius of (1), which can replace calcium ion Ca²⁺But this replacement adds one charge because of the praseodymium Pr³⁺Valence ratio of calcium ion Ca²⁺Has one more valence. To balance the charge, the titanium ion Ti with a valence of 4+ may be replaced by a positive ion with a valence of 3+⁴⁺The position of (a). Because of the aluminum ion Al having a valence of 3+³⁺Ga ion Ga³⁺And indium ion In³⁺Each of which can replace the titanium ion Ti⁴⁺For a praseodymium ion Pr from³⁺Replacing a calcium ion Ca²⁺Can be formed by ametal ion of Al, Ga or in³⁺、Ga³⁺、In³⁺By replacing a titanium ion Ti⁴⁺So that the praseodymium ion Pr balances the charge³⁺Calcium titanate CaTiO which may be present as matrix crystal₃In (1). Further, it is presumed that the zinc ion Zn is present due to the ionic radius thereof²⁺Or magnesium ion Mg²⁺Can replace titanium ion Ti⁴⁺The position of (a). However, because of the zinc ion Zn²⁺Or magnesium ion Mg²⁺Are both positive ions with a valence of 2+, so this substitution reduces both charges. Thus, when formed from a zinc or magnesium ion Zn²⁺、Mg²⁺By replacing a titanium ion Ti⁴⁺In the case of (1), two praseodymium ions Pr may be used³⁺Ca replacing two calcium ions²⁺To balance the charge. Moreover, due to its ionic radiusLithium ion Li⁺Sodium ion Na⁺Or potassium ion K⁺Can replace Ca ion²⁺The position of (a). However, since lithium ion Li⁺Sodium ion Na⁺And potassium ion K⁺Are all positive ions with a valence of 1+, so the substitution reduces one charge. Thus, when Li is a lithium, sodium or potassium ion⁺、Na⁺、K⁺Replacing a calcium ion Ca²⁺At the position of (1), there can be one praseodymium ion Pr³⁺Replacing a calcium ion Ca²⁺To balance the charge. Thus, each of the second additives has a stable praseodymium ion Pr³⁺Thus, it contributes to emitting light with a greater intensity than a fluorescent material to which these second additives are not added. In the phosphor to which only praseodymium Pr is added without adding these second additives, a certain amount of calcium Ca is released from the crystal lattice thereof to balance the charge, but thus a corresponding amount of defects are generated in the crystal lattice, thereby decreasing the emission intensity of the phosphor.

Here, the addition amount of praseodymium Pr is preferably in the range of 0.008 mol% to 0.023 mol%.

In addition, the second additive preferably includes 0.1 mol% to 1.0 mol% of aluminum Al with respect to 100 mol% of the matrix crystal. Since the amount of aluminum Al added is suitable, the phosphor can emit high luminance, for example, at least 50cd/m even when the phosphor is excited by a low-voltage electron beam²Of (2) is detected. Particularly preferably, the amount of aluminum Al added is in the range of 0.2 mol% to 0.5 mol%. In the latter case, the fluorescent material may emit light even when the fluorescent material is excited by a low-voltage electron beamHigher luminance, e.g. at least 70cd/m²Of (2) is detected. In general, it is desirable that the phosphor emits light with a luminance of at least 50cd/m²Particularly desirably, the luminance is at least 70cd/m²。

In addition, the second additive preferably comprises at least 0.07 mol% of gallium Ga with respect to 100 mol% of the host crystal. Since the fluorescent material includes a sufficient amount of gallium Ga, the fluorescent material can emit a high luminance even when the fluorescent material is excited by a low-voltage electron beamE.g. at least 50cd/m²Of (2) is detected.

In addition, the second additive preferably includes at least 0.13 mol% of zinc Zn with respect to 100 mol% of the matrix crystal. Since the phosphor includes zinc Zn in a sufficient amount, the phosphor can emit high luminance, for example, at least 50cd/m, even when the phosphor is excited by a low-voltage electron beam²Of (2) is detected. Particularly preferably, the amount of zinc Zn added is not less than 0.66 mol%. In the latter case, the phosphor may emit a higher luminance, e.g., at least 70cd/m²Of (2) is detected.

In addition, the second additive preferably includes at least 0.07 mol% of magnesium Mg with respect to 100 mol% of the matrix crystal. Since the phosphor material comprises a sufficient amount of magnesium Mg, the phosphor material can emit a high luminance of, for example, at least 50cd/m even when excited by a low-voltage electron beam²Of (2) is detected. Particularly preferably, the amount of magnesium Mg added is not less than 0.1 mol%. In the latter case, the phosphor may emit a higher luminance, e.g., at least 70cd/m²Of (2) is detected.

In addition, CaTiO is added to 100 mol% of the matrix crystal₃Pr, M phosphor also preferably includes at least 0.5 mol% of lithium Li. Since (a) at least one of aluminum Al, gallium Ga, indium In, zinc Zn, magnesium Mg, sodium Na, and potassium K, and (b) lithium Li can improve the emission luminance of the fluorescent material, the fluorescent material can emit a higher luminance of, for example, at least 70cd/m than a fluorescent material including only one or more of aluminum Al, gallium Ga, indium In, zinc Zn, magnesium Mg, sodium Na, and potassium K²Of (2) is detected.

In addition, CaTiO₃Pr, M phosphor preferably comprises a plurality of second additives M selected from the group consisting of aluminum Al, gallium Ga, zinc Zn, magnesium Mg, indium In, sodium Na, and potassium K, which are added together In the host crystal. In this case, it is desirable that the amount of each second additive added to the matrix crystals falls within the above-described preferred range when it is added alone.

The invention also relates to a process for the manufacture of the CaTiO according to the first aspect of the invention₃Pr, M fluorescent material, the method comprising the steps of: mixing ofSynthesizing the following (a), (b) and (c)Mixing the three materials with each otherto form a mixture, wherein (a) is a raw material of a matrix crystal for providing calcium titanate CaTiO as a matrix crystal₃(b) a first additive raw material comprising praseodymium (Pr), and (c) at least one second additive raw material comprising at least one of aluminum (Al), gallium (Ga), indium (In), zinc (Zn), magnesium (Mg), sodium (Na), and potassium (K); and a sintering (sintering) step of sintering the mixture at a first preselected temperature in the range 1050 to 1250 ℃, particularly preferably 1050 to 1200 ℃, most preferably 1100 to 1150 ℃.

In the method, a host crystal raw material, a first additive raw material, and a second additive raw material or material are mixed with each other in a mixing step, and the mixture thus obtained is sintered at a preselected temperature in the range of 1050 ℃ to 1250 ℃ in a sintering step. Therefore, the method manufactures an oxide fluorescent material which can have a long life expectancy and can emit light of high brightness even when it is excited by a low-voltage electron beam. More specifically, since the phosphor is sintered at a very low temperature as described above, the phosphor emits light of high luminance (e.g., at least 50 cd/m) when excited by a low-voltage electron beam²) The brightness is obtained by sintering conventional CaTiO at a higher temperature, for example about 1300 deg.C₃The luminescent brightness of the fluorescent material is at least twice. In addition, the fluorescent material produced by the method is more conventional than SrTiO₃Pr, Al phosphors are less degraded.

Preferably, CaTiO₃The method of manufacturing the Pr, M phosphor further comprises a calcination step wherein the mixture is calcined to a calcined material at a second preselected temperature prior to the sintering step, the second preselected temperature being in the range of 800 ℃ to 1000 ℃. According to this feature, praseodymiumPr as the first additive and the second additive such as aluminum Al can be more uniformly diffused into calcium titanate CaTiO as the matrix crystal₃In (1). Therefore, the luminance brightness can be improved by at least 20% as compared with the case where the calcination step is not performed. If the distribution of the praseodymium Pr concentration is not uniform, i.e., the praseodymium Pr concentration is excessively high or low, the concentration of the praseodymium Pr is not uniformA so-called "concentration quenching" phenomenon can occur at one or more high concentration portions, and luminescence centers may be lacking at one or more low concentration portions. This may result in a decrease in the emission luminance of the fluorescent material, thereby decreasing the intensity of light.

In addition, CaTiO is preferable₃The manufacturing method of the Pr, M fluorescent material also comprises the following steps: a first milling step wherein the calcined material is milled to particles having a diameter of about 1 μm, and wherein the sintering step comprises sintering the milled calcined material; a second milling step, wherein the sintered material is milled into particles having a diameter of about 3 μm; a sieving step in which the milled sinter is washed and sievedSo as to remove unreacted components and obtain a fluorescent material comprising a water component; a drying step in which the obtained fluorescent material is dried to remove a water component; and a pulverization step in which the dried fluorescent material is pulverized into particles having a diameter of about 3 μm.

In addition, it is preferable that the first additive raw material includes praseodymium chloride PrCl₃. According to this feature, the method of manufacturing the fluorescent material forms such CaTiO₃Pr, M fluorescent material whose luminous brightness is other CaTiO using other praseodymium compounds₃At least twice the luminous brightness of Pr, M phosphors. More specifically, for example, praseodymium chloride PrCl is generally used₃Praseodymium carbonate Pr (CO)₃)₃Praseodymium nitrate Pr (NO)₃)₃And praseodymium oxide Pr₆O₁₁As praseodymium compounds to obtain CaTiO₃Pr, M fluorescent material. However, when praseodymium chloride PrCl is used₃As praseodymium Pr source to obtain CaTiO₃Pr, M phosphor, the phosphor thus obtained can emit light with the highest luminance, which is about twice the luminance of the phosphor obtained using carbonate or nitrate and about ten times the luminance of the phosphor obtained using oxide.

Drawings

The foregoing and other objects, features, advantages and technical and industrial significance of this invention will be better understood from the following detailed description of the presently preferred embodiments of the invention when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a flow chart showing a method for manufacturing a fluorescent material according to the present invention;

fig. 2 is a partially cut-away view of the entire structure of a vacuum fluorescent display, which is one example of a fluorescent display device according to the present invention;

FIG. 3 is an enlarged plan view of a portion of the display surface of the vacuum fluorescent display showing the layer of phosphor material;

FIG. 4 is an enlarged cross-section of a portion of a vacuum fluorescent display showing the structure of the display;

fig. 5 is a graph showing a relationship between the amount of aluminum Al and the luminance obtained from the fluorescent material;

fig. 6 is a graph showing a relationship between the amount of gallium Ga and luminance obtained from another fluorescent material as another embodiment of the present invention;

fig. 7 is a graph showing a relationship between the amount of indium In and luminance obtained from another fluorescent material as another embodiment of the present invention;

FIG. 8 is a graph showing the relationship between the amount of magnesium Mg and the luminance obtained from another fluorescent material as another embodiment of the present invention;

fig. 9 is a graph showing a relationship between the amount of zinc Zn and luminance obtained from another fluorescent material as another embodiment of the present invention;

FIG. 10 is a graph showing a relationship between a sintering temperature and luminance obtained from another fluorescent material as another embodiment of the present invention;

FIG. 11 is a graph showing a relationship between a sintering temperature and luminance obtained from another fluorescent material as another embodiment of the present invention; and

fig. 12 is a graph showing a relationship between various compounds of praseodymium Pr and luminance obtained from various fluorescent materials including other fluorescent materials as another embodiment of the present invention.

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It is noted, however, that the drawings may be more or less simplified or intentionally modified and that, as such, the dimensional proportions and/or shapes of the individual elements and/or parts of the invention may not be drawn precisely.

Fig. 1 is a flowchart showing a method of manufacturing a fluorescent material according to the present invention. CaTiO will be described below with reference to FIG. 1₃Pr, Al fluorescent material, which is an example of the fluorescent material of the present invention. First, in the raw material mixing step P1, an appropriate compound such as calcium carbonate CaCO is weighed as an initial raw material of the fluorescent material to be manufactured, depending on the composition of the fluorescent material₃Titanium oxide TiO₂Praseodymium chloride PrCl₃And aluminum hydroxide Al (OH)₃And mixed well with, for example, a ball mill or a mortar. The mixing ratios were as follows: Ca/Ti 0.99 (molar ratio), Pr to CaTiO₃In a proportion of 0.05 to 0.3 mol%, Al relative to CaTiO₃The proportion of (B) is 0 to 0.5 mol%.

Subsequently, in the calcination step P2, the mixed raw material (i.e., the mixture) is put into, for example, a crucible made of alumina having a purity of at least 99.5%, and subjected to calcination treatment at, for example, atmospheric pressure at a temperature of up to about 900 ℃ for about 10 hours. The calcined material obtained is then milled in a first milling step P3, for example in an alumina mortar, into particles having an average diameter of about 1 μm.

Next, in a sintering step P4, the milled calcined material is placed in, for example, an alumina crucible and subjected to a sintering treatment at, for example, atmospheric pressure, at a temperature of up to about 1050 ℃ to about 1150 ℃ for about 3 hours. Thus, the above-mentioned starting materials react with each other according to the following chemical reaction formula (1), and CaTiO as a fluorescent material is synthesized₃:Pr，Al：

...(1)

Subsequently, in a second milling step P5, the synthesized fluorescent material is milled in, for example, an alumina mortar into particles having an average diameter of about 3 μm.

Next, in a washing step P6, the ground phosphor particles are dispersed in water in order to dissolve the water-soluble residual material. Praseodymium chloride PrCl as one of the starting materials₃Water-soluble, while synthetic fluorescent materials and other raw materials are insoluble in water. Thus, only the unreacted praseodymium chloride PrCl is present₃Dissolved in water.

Subsequently, in the screening step P7, the fluorescent material dispersed in water is screened using, for example, a #300 mesh screen to remove large particles, and then the screened suspension is left for an appropriate time to precipitate small particles of the fluorescent material. After said time, the supernatant is removed by pipetting, for example, with a pipette. Thereby removing water-soluble residual materials (i.e., water-soluble components of the starting materials) included in the supernatant. The steps P6, P7 may be repeated as many times as necessary in order to completely remove the water-soluble residual material. Next, in the drying step P8, the fluorescent material particles remaining after the removal of the supernatant liquid are dried at, for example, a temperature of about 120 ℃ for about 5 hours. Subsequently, in the pulverization step P9, the obtained solid material was pulverized into particles having a diameter of about 3 μm in, for example, an alumina mortar. Thereby obtaining CaTiO₃Pr, powder of Al fluorescent material.

The evaluation results of the characteristics of the fluorescent material manufactured by the above-described method are explained below. For this purpose, a phosphor powder is mixed with an appropriate amount of indium oxide In₂O₃The powders are mixed so as to increase the electrical conductivity of the phosphor powder, and are also mixed with an organic binder and a carrier such as an organic solvent so as to prepare a paste of the phosphor. The mixed indium oxide In is appropriately measured depending on the electrical conductivity of the fluorescent material powder itself and the required electrical conductivity of the layer formed of the fluorescent material₂O₃Amount of powder. For example, about 5 wt.% to about 15 wt.% indium oxide In₂O₃The powder was mixed with 100 wt% of the phosphor powder. The fluorescence thus preparedThe material paste is used, for example, for a display surface of a display device so that a phosphor layer of an appropriate thickness is formed. The phosphor layer thus formed was evaluated. More specifically, the present invention is described in detail,the vacuum fluorescent display 10 having the structure shown in fig. 2, 3, and 4 was evaluated.

Fig. 2 shows a vacuum fluorescent display 10 as one example of the fluorescent display device according to the present invention. In this figure, the vacuum fluorescent display 10 includes a backplane 12 provided with a layer of phosphor material 22; a frame-shaped glass spacer 14; a transparent glass cover plate 16; a plurality of anode terminals 18 p; a plurality of gate terminals 18 g; and two cathode terminals 18 k. The fluorescent material layer 22 includes a plurality of fluorescent patterns respectively located at a plurality of positions. The base plate 12 is made of an electrically insulating material such as glass, ceramic, or enamel. The bottom plate 12 and the glass cover plate 16 are sealed to each other by a glass spacer 14 to provide a long flat box-like airtight container having a vacuum space therein.

The substrate 12 has a display surface 20 with a layer 22 of phosphor material defining phosphor patterns, each of which is surrounded by a grid 24 and an auxiliary electrode 26. The auxiliary electrode 26 is electrically insulated from the gate electrode 24, and the auxiliary electrode 26 is common to all the fluorescent patterns. The gate 24 and auxiliary gate 26 are connected to the gate terminal 18g by

gate links

30, 32, respectively, provided on the display surface 20 and by respective terminal pads 28 provided along the long sides of the surface 20.

Two end members 34 (only one end member 34 is shown in fig. 2) are fixed to the lengthwise opposite ends of the bottom surface 12, each of which includes a corresponding one of the two cathode terminals 18k described above, and a fixed holder 36 that cooperates with a support member, not shown, to support a plurality of filaments (i.e., direct-heated cathodes) 38 that serve as direct-heated cathodes so that the filaments 38 are linear, parallel to the lengthwise direction of the bottom plate 12, and are located at a predetermined height above the display surface 20, i.e., the fluorescent material layer 22. Each filament 38 is composed of, for example, a tungsten (W) filament, the surface of which is coated with an electron emission layer, for example, a solid solution of an alkaline earth metal oxide having a low work function such as BaO, SrO, CaO. The vacuum fluorescent display 10 includes, not shown, an getter for increasing the degree of vacuum of the inner space of the airtight container; and an exhaust pipe or hole, not shown, for exhausting gas from the inner space of the container, thereby making the inner space vacuum.

Fig. 3 shows a portion of the display surface 20 in enlarged view, and fig. 4 shows a portion of the base plate 12 in enlarged view in cross section. A plurality of anode wirings 40 each composed of, for example, a conductive thick film, and connected to a corresponding one of the anode terminals 18p are provided on the display surface 20. An electrically insulating layer 44, which is composed of a glass thick film and has a plurality of through holes 42 at respective appropriate positions, is fixed on the anode wiring 40. A plurality of anodes 46, each consisting of, for example, a graphite sheet or film, having a size slightly larger than the fluorescent pattern of the corresponding fluorescent material layer 22, are disposed on the insulating layer 44. Anodes 46 are electrically connected to respective anode connections 40 through respective vias 42 in insulating layer 44. A phosphor layer 22 is formed on the anode 46. Each phosphor pattern of the layer of phosphor material 22 is surrounded by rib-like walls 48, 50, each of which is comprised of, for example, a thick glass film. Each of the above-described gate 24 and auxiliary gate 26 is composed of, for example, a conductive thick film, and is disposed on top of the corresponding rib wall 48, 50.

In the vacuum fluorescent display 10 constructed as described above, thermal electrons emitted at 0V by the direct heating cathode 38 are accelerated by the grid 24 to which a positive voltage of, for example, 20V is applied. Thus, for example, in the case where an accelerating voltage is continuously applied to the gate electrode 24, i.e., "scanning" the same 24, and at the same time, a positive voltage is selectively applied to the respective anode wirings 40 connected to the desired fluorescent pattern of the fluorescent material layer 22, so that the thermal electrons collide with the desired fluorescent pattern in synchronization with the scanning of the gate electrode 24 to cause the fluorescent pattern to emit light. If the anode line 40 to which the positive voltage is selectively applied is changed every time the gate 24 is scanned, a desired fluorescence display image can be continuously obtained. However, the fluorescent material is evaluated in such a manner that the brightness of the light is measured under the condition that a positive voltage is continuously applied to the fluorescent pattern of the fluorescent material layer 22 and the fluorescent pattern thus continuously emits light.

FIG. 5 shows the results of evaluation of the composition of a fluorescent material to which 100 mol% of CaTiO calcium titanate is to be added₃The amount of praseodymium Pr in the solution is changed from 0mol percent to 0.10mol percent, and 100mol percent of calcium titanate CaTiO is added₃The amount of aluminum Al in the alloy varies from 0 mol% to 1.5 mol%. The initial brightness of red light having a wavelength of about 614 nm, which is the peak wavelength of the fluorescent material, was measured under the condition that the vacuum fluorescent display 10 was excited at a voltage of 26V and operated at a duty cycle of 1/12. As shown in FIG. 5, when the amount of aluminum added was 0 mol% or 1.5 mol%, at least 50cd/m could not be obtained over the entire range of the amount of praseodymium Pr added²High brightness of (2). However, when the amount of Al added varies from 0.1 mol% to 1.0 mol%, at least 50cd/m can be obtained over the entire range where the amount of Pr is from 0.003 mol% to 0.05 mol%²High brightness of (2). In particular, the phosphor emits at least 70cd/m when the amount of praseodymium added varies within the range of 0.008 mol% to 0.023 mol%²Sufficiently high to be observed by the human eye.

In the range where the amount of praseodymium Pr exceeds 0.02 mol%, the brightness increases with the amount of praseodymium Pr addedBut a gradually decreasing trend. In particular, although not shown in fig. 5, it can be easily presumed from the figure that the luminance remains relatively low in the range where the praseodymium Pr exceeds 0.1 mol%, that is, not higher than 20cd/m². Therefore, it is understood that if the concentration of praseodymium Pr added is too low or too high, high luminance cannot be obtained.

In addition, as shown in FIG. 5, when the amount of praseodymium Pr added is changed from 0.005 mol% to 0.05 mol%, if the amount of aluminum Al added is changed in the range of 0.1 mol% to 1.0 mol%, at least 50cd/m can be obtained²High brightness of (2). In particular, when the amount of aluminum Al is about 0.3 mol%, at least 100cd/m equivalent to that of the conventional sulfide fluorescent material can be obtained²The brightness of (2).

Also, for the fluorescent material, the expected half-life thereof, i.e., the time required for the luminance to decrease to half of the original luminance, can be measured under the same conditions as described aboveProvided that the vacuum fluorescent display 10 was excited at a voltage of 26V and operated at a duty cycle of 1/12. The measurements show that all compositions of the fluorescent material emitting high brightness show an expected half-life of more than 1000 hours, compared to SrTiO₃The expected half-life of the fluorescent material of less than 100 hours is much longer.

In short, the fluorescent material, i.e. CaTiO₃Pr, Al fluorescent material comprises: calcium titanate CaTiO as matrix crystals₃0.003 mol% to 0.05 mol% of praseodymium Pr as an activator, and aluminum Al as an additive. Therefore, the lifetime expectancy ratio of the fluorescent material SrTiO₃The fluorescent material is long, and when the fluorescent material is excited by a low-voltage electron beam, high brightness enough to be observed with the naked eye can be obtained.

FIG. 6 shows a graph for CaTiO₃Pr, measurement of the initial brightness of Ga phosphors, in which aluminum Al is replaced by gallium Ga in an amount of 0.1 mol% to 0.5 mol%. The CaTiO₃Pr, the Ga fluorescent material comprises 0.01mol percent of praseodymium Pr. As is apparent from FIG. 6, if the amount of Ga added is not less than the lower limit of 0.07 mol%, at least 50cd/m can be obtained²Sufficiently high brightness. However, this experiment cannot illustrate the upper limit of the appropriate range for adding gallium Ga. It can be expected that CaTiO will be present even if the range of Ga exceeds 0.5 mol%₃Pr, Ga phosphors will still exhibit a brightness comparable to or higher than the high brightness described above.

FIG. 7 shows a graph for CaTiO₃Pr, measurement result of initial luminance of In fluorescent material In which aluminum Al is replaced with indium In of 0.3 mol% to 0.6 mol%. The CaTiO₃Pr, the In fluorescent material comprises 0.01mol percent of praseodymium Pr. In FIG. 7, if the data point would correspond to the addition of 0 mol% indium InIn comparison with the other two data points corresponding to the addition of 0.3 mol% and 0.6 mol% indium, it is evident that the addition of indium In enhances the brightness. It is expected that if the amount of indium added is not less than 0.2 mol%, at least 50cd/m can be obtained²High brightness of (2). However, this experiment cannot specify the upper and lower limits of the appropriate range for adding indium In. Similar to gallium Ga, it can be expected that even if the range of indium In exceeds 0.6 mol%, CaTiO₃:Pr, In fluorescent materials will still show higher brightness.

FIG. 8 shows a graph for CaTiO₃Pr, measurement of initial luminance of Mg fluorescent material in which aluminum Al is replaced with 0.1 mol% to 0.5 mol% of magnesium Mg. The CaTiO₃Pr, the Mg fluorescent material comprises 0.01mol percent of praseodymium Pr. The fluorescent material is prepared by using magnesium nitrate Mg (NO)₃)₂Synthesized asa magnesium Mg source. As is apparent from FIG. 8, if the amount of magnesium Mg added is not less than the lower limit of 0.07 mol%, at least 50cd/m can be obtained²Sufficiently high brightness. However, this experiment cannot illustrate the upper limit of the appropriate range for adding magnesium Mg. It can be expected that even if the Mg content exceeds 0.5 mol%, CaTiO₃Pr, Mg phosphor will still show higher characteristics because the brightness increases with the addition of Mg in the curve of fig. 8.

FIG. 9 shows a graph for CaTiO₃Pr, measurement of initial luminance of Zn fluorescent material, in which aluminum Al is replaced with zinc Zn of 0.13 mol% to 2.65 mol%. The CaTiO₃Pr, Zn fluorescent material contains 0.01mol percent of praseodymium Pr. The fluorescent material is prepared by using zinc nitrate Zn (NO)₃)₂Synthesized as a zinc Zn source. As is apparent from FIG. 9, if the amount of zinc Zn added is not less than the lower limit of 0.13 mol%, at least 50cd/m can be obtained²Sufficiently high brightness. However, this experiment cannot illustrate the upper limit of the appropriate range for adding zinc Zn. It can be expected that CaTiO will be present even if the Zn content exceeds 2.65 mol%₃Pr, Zn fluorescent materials will still show higher characteristics because the brightness increases with increasing amount of zinc Zn addition in the graph of fig. 9.

In addition, another fluorescent material in which aluminum Al was replaced with zinc Zn and lithium Li, but the measurement results of the initial luminance thereof were not shown in the figure, was evaluated. When 2.65 mol% Zn and 0.5 mol% Li were added, the phosphor showed about 131cd/m, as compared with the case where only 2.65 mol% Zn was added²Very high brightness. In this example, we can say that praseodymium Pr is the first additive, zinc Zn is the second additive, and lithium Li is the third additive.

FIG. 10 shows a graph derived from CaTiO₃Pr, Li fluorescent materialThe relation between sintering temperature and brightness obtained for the phosphor material, in which aluminum Al is replaced by lithium Li. The CaTiO₃Pr, Li fluorescent material comprises0.01 mol% of praseodymium Pr. The fluorescent material is prepared by using CaTiO in 100 mol% of calcium titanate₃0.5 mol% of lithium carbonate Li₂CO₃Synthesized as a lithium Li source. As is apparent from FIG. 10, if the sintering temperature is 1200 deg.C, the luminance is maintained at 30cd/m². However, if the sintering temperature is 1150 ℃ and sufficiently lower than 1200 ℃, the luminance is increased to 70cd/m²I.e. 30cd/m²Twice as much; and can attain at least 50cd/m even if the sintering temperature is 1000 DEG C²High brightness of (2).

When the above-mentioned optimum sintering conditions are applied to CaTiO to which lithium Li is added₃Pr, Li phosphor, about 160cd/m was obtained from a phosphor comprising 2 mol% lithium Li²Very high brightness of; approximately 130cd/m was obtained from a phosphor comprising 3 mol% lithium Li²Very high brightness of; and about 100cd/m was obtained from a phosphor comprising 6 mol% lithium Li²Very high brightness. These fluorescent materials each show a relationship between sintering temperature and luminance similar to that shown in fig. 10, which is not shown in the drawing.

Briefly, in this example, in the mixing step P1, a host crystal raw material, a praseodymium Pr source, and a lithium Li source are mixed with each other; and, in a sintering step P4, sintering the mixture thus obtained at a temperature in the range 1050 ℃ to 1150 ℃. CaTiO thus obtained₃Pr, Li oxide phosphor lifetime expectancy ratio SrTiO₃Pr, Al fluorescent material is long, and even if CaTiO is excited by a low-voltage electron beam₃Pr, Li fluorescent material, which can still emit light of high brightness. For each of the other second additives (i.e. Al, Ga, In, Mg, Zn) than li, fig. 5 to 9 show the measurements obtained from the respective fluorescent materials sintered at a temperature In the range 1050 to 1150 c, which can be considered to be optimal for the fluorescent materials.

FIG. 11 corresponds to the relationship shown in FIG. 10Goes out of CaTiO₃Pr, the relationship between sintering temperature and brightness obtained for Al phosphors. These CaTiO compounds₃Pr, the Al phosphor included 0.3 mol% Al and different amounts of Pr added, i.e., 0.0075 mol%, 0.01 mol%, and 0.02 mol%. As shown in FIG. 11, the luminance of the phosphor sintered at 1300 ℃ was maintained at about 5cd/m, although the relationship was more or less different from each other according to the addition amount of praseodymium Pr²Whereas the brightness of the phosphor sintered at 1250 c, which is substantially lower than 1300 c, is significantly increased. For example, the luminescent brightness of the phosphor including 0.0075 mol% of praseodymium Pr and sintered at 1250 ℃ is about 50cd/m²Which is about ten times the brightness of the fluorescent material sintered at 1300 c. In addition, if the sintering temperature is 1200 ℃, the luminance of the phosphor including 0.02 mol% of praseodymium Pr is about 80cd/m²Is composed of 0.01The luminance of the phosphor of mol% praseodymium Pr is about 100cd/m²And the luminance of the phosphor material including 0.0075 mol% of praseodymium Pr is about 120cd/m²。

In particular, when the sintering temperature is in the range of 1100 ℃ to 1150 ℃, with respect to the fluorescent material including 0.01 mol% or 0.02 mol% of praseodymium Pr, not less than 120cd/m is obtained²Brightness of (d); for a phosphor even comprising 0.0075 mol% of praseodymium Pr, a value of not less than 90cd/m is obtained²The brightness of (2).

However, if the sintering temperature is too low, high brightness cannot be obtained. For example, if the sintering temperature is 1000 ℃ and the luminance is maintained at most about 30cd/m². However, when the sintering temperature was 1050 ℃, at least 50cd/m was obtained for each of the three compositions as shown in FIG. 11²The brightness of (2). Although not shown, a similar trend may be observed for other fluorescent materials including other elements or additives, although the obtained data are more or less different from each other according to the kind of the additive. As is apparent from those data, the sintering temperature preferably falls within the range of 1050 ℃ to 1250 ℃. In particular, when the sintering temperature is in the range of 1100 ℃ to 1150 ℃, it is advantageous to obtain not less than 100cd/m²Very high brightness. Most importantly, for fluorescence including 0.01 mol% or 0.02 mol% praseodymium PrThe material, when sintered at temperatures in the range of 1100 ℃ to 1200 ℃, will advantageously achieve very high brightness.

FIG. 12 shows various praseodymium compounds as praseodymium Pr sources and various CaTiO compounds synthesized from the praseodymium compounds₃Pr, the relationship between the brightness obtained by Al phosphors. Each CaTiO₃Pr and Al fluorescent material contains 0.01mol percent of praseodymium Pr and 0.3mol percent of aluminum Al. Evaluation of the results shown in FIG. 12 clearly shows that the results obtained from the inclusion of chloride (e.g., praseodymium chloride PrCl)₃) Can obtain at least 100cd/m²And includes carbonates (e.g., praseodymium carbonate Pr (CO)₃)₃) Or nitrate (e.g. praseodymium nitrate Pr (NO)₃)₃) The luminance of the phosphor material of (1) was maintained at about 60cd/m²And including oxides (e.g., praseodymium oxide Pr)₆O₁₁) The luminance of the phosphor of (a) is kept low, i.e. about 10cd/m². Thus, it will be appreciated that the praseodymium Pr source is preferably its chloride rather than its oxide.

Although the preferred embodiments of the present invention have been described with reference to the accompanying drawings, it is to be understood that other changes, modifications, and improvements may be made by those skilled in the art without departing from the scope of the present invention.

Claims

1. CaTiO₃Pr, M fluorescent material comprising:

100 mol% of calcium titanate CaTiO₃As a host crystal;

0.003 to 0.05 mol% of praseodymium Pr added to the matrix crystal as a first additive; and

at least one of aluminum Al, gallium Ga, indium In, zinc Zn, magnesium Mg, sodium Na, and potassium K, which is added to the host crystal as a second additive M.

2. CaTiO according to claim 1₃Pr, M fluorescent material, wherein the second additive comprises 0.1 mol% to 1.0 mol% of aluminum Al with respect to 100 mol% of the host crystal.

3. CaTiO according to claim 1₃Pr, M fluorescent material, wherein the second additive comprises at least 0.07 mol% of gallium Ga with respect to 100 mol% of the host crystal.

4. CaTiO according to claim 1₃Pr, M fluorescent material, wherein the second additive comprises 0.3 mol% to 0.6 mol% indium In with respect to 100 mol% of the host crystal.

5. CaTiO according to claim 1₃Pr, M fluorescent material, wherein the second additive comprises at least 0.13 mol% of zinc, Zn, relative to 100 mol% of the host crystal.

6. CaTiO according to claim 1₃Pr, M fluorescent material, wherein the second additive comprises at least 0.07 mol% of magnesium Mg with respect to 100 mol% of the host crystal.

7. CaTiO according to claim 1₃Pr, M phosphor, further comprising at least 0.5 mol% of lithium Li, which is added as a third additive to 100 mol% of the host crystal.

8. CaTiO according to claim 1₃Pr, M fluorescent material, wherein 0.008 mol% to 0.023 mol% of praseodymium Pr is added as the first additive to the host crystal.

9. CaTiO according to claim 1₃Pr, M fluorescent material comprising a plurality of said second additives M selected from the group consisting of aluminum Al, gallium Ga, indium In, zinc Zn, magnesium Mg, indium In, sodium Na, and potassium K, and which are added together to said host crystal.

10. A fluorescent display device (10) comprising a CaTiO according to any one of claims 1 to 9₃Pr, M fluorescent material (22) as a light source.

11. A method of making a CaTiO according to any one of claims 1 to 9₃Pr, M fluorescentA method of optical material, the method comprising the steps of:

a mixing step in which three materials of (a), (b) and (c) below, which are a raw material of a matrix crystal for providing calcium titanate CaTiO as the matrix crystal, are mixed with each other into a mixture₃A first additive raw material containing praseodymium Pr, and (c) at least one second additive raw material containing at least one of aluminum Al, gallium Ga, indium In, zinc Zn, magnesium Mg, sodium Na, and potassium K; and

a sintering step, wherein the mixture is sintered at a first preselected temperature, said first preselected temperature being in the range 1050 ℃ to 1250 ℃, particularly preferably 1050 ℃ to 1200 ℃, most preferably 1100 ℃ to 1150 ℃.

12. The method of claim 11, further comprising a calcining step, wherein prior to said sintering step, said mixture is calcined to a calcined material at a second preselected temperature, said second preselected temperature being in the range of 800 ℃ to 1000 ℃.

13. The method of claim 12, further comprising

A first milling step wherein the calcined material is milled to particles having a diameter of about 1 μm, and wherein the sintering step comprises sintering the milled calcined material;

a second milling step wherein the sintered material is milled into particles having a diameter of about 3 μm;

a sieving step in which the sintered material subjected to grinding is washed and sieved so as to remove unreacted components therefrom and obtain the fluorescent material including a water component;

a drying step of drying the obtained fluorescent material to remove the water component; and

a pulverization step in which the dried fluorescent material is pulverized into particles having a diameter of about 3 μm.

14. The method of claim 11 wherein said first additive source comprises praseodymium chloride (PrCl)₃。